1. Field of the Invention
The present invention relates to a liquid ejection head for ejecting liquid.
2. Description of the Related Art
An inkjet recording apparatus designed to eject ink and record an image on a recording medium generally includes a liquid ejection head mounted therein to eject ink. Mechanisms employing pressure chambers whose capacities can be expanded and contracted by means of piezoelectric elements are known as mechanisms for causing a liquid ejection head to eject ink. With such a mechanism, as each of the piezoelectric elements is deformed due to the voltage applied thereto, the related pressure chamber is contracted to eject ink in the pressure chamber from an ejection port formed at an end of the pressure chamber. As a type of liquid ejection head having such a mechanism, shear mode type liquid ejection heads having pressure chambers, each having one or two inner wall surfaces formed by using so many piezoelectric elements, are known. Such a shear mode type liquid ejection head is designed to contract each of the pressure chambers by shear deformation of the piezoelectric elements of the pressure chamber unlike instances where piezoelectric elements are subjected to contraction deformation and expansion deformation.
Inkjet recording apparatus for industrial applications are required to be able to use high viscosity liquid. For a liquid ejection head to eject high viscosity liquid, the ejection head is required to provide a large ejection force. So-called Gould type liquid ejection heads including pressure chambers each of which is formed by using a cylindrical piezoelectric member representing a circular or rectangular cross section have been proposed to meet the requirement. A Gould type liquid ejection head is so designed that each of the pressure chambers is expanded and contracted as the piezoelectric member is deformed by expansion and contraction respectively in inward and outward directions (radial directions) relative to the center of the pressure chamber. In a Gould type liquid ejection head, all the wall surfaces of each pressure chamber are deformed and the deformations boost the ejection force of the liquid ejection head. Therefore, Gould type liquid ejection heads can provide a larger liquid ejection force if compared with shear mode type liquid ejection heads in which one or two wall surfaces of each of the pressure chambers are formed by using piezoelectric elements.
For a Gould type liquid ejection head to provide a higher resolution, a plurality of ejection ports need to be arranged highly densely. Then, as a result, pressure chambers that correspond to the respective ejection ports need to be arranged highly densely. Japanese Patent Application Laid-Open No. 2007-168319 discloses a method of manufacturing a Gould type liquid ejection head in which pressure chambers can be formed highly densely.
With the manufacturing method disclosed in Japanese Patent Application Laid-Open No. 2007-168319, firstly a plurality of grooves that extend in the same direction are formed for each piezoelectric plate. Subsequently, the plurality of piezoelectric plates are aligned in terms of the directions of their grooves and laid one on the other. The piezoelectric plates are then cut in a direction perpendicular to the running direction of the grooves. The groove parts of the cut piezoelectric plates constitute inner wall surfaces of pressure chambers. Thereafter, the piezoelectric member existing between any adjacently located pressure chambers is removed to a certain depth in order to separate the pressure chambers. Then, a supply channel plate and an ink pool plate, and a printed circuit board and a nozzle plate are connected respectively to the top and to the bottom of the piezoelectric plates having complete pressure chambers to produce a complete liquid ejection head. With this manufacturing method, pressure chambers can be arranged into a matrix of pressure chambers. In other words, pressure chambers can be arranged highly densely. Additionally, with this manufacturing method, pressure chambers can be formed highly accurately because forming grooves in piezoelectric plates ensures a better machinability than cutting holes in piezoelectric plates.
The pressure chambers of a liquid ejection head manufactured by the method disclosed in Japanese Patent Application Laid-Open No. 2007-168319 are separated from each other by spaces. In other words, the wall sections of each of the pressure chambers are formed independently. Then, as a result, the liquid ejection head cannot secure a satisfactory level of rigidity particularly when the pressure chambers are made long (high) for the purpose of ejecting highly viscous liquid (in other words for the purpose of providing a large force for ejecting liquid). As the rigidity of the liquid ejection head falls, the structures (walls) forming the pressure chambers become easily breakable so that they can easily give rise to a situation where liquid can no longer be ejected.